1. Field of the Invention
This invention relates to x-ray method and apparatus and more particularly to a novel and improved method of taking radiographs and an apparatus for carrying out the method.
In one typical type of medical diagnostic procedure using radiographs, the patient is positioned on a radiographic table. A light-tight X-ray film cassette which carries the radiographic film is positioned in a tray beneath the surface of the table. An X-ray tube carried on a tower or ceiling-mounted column is then positioned over the patient and aligned with that portion of the patient's body which is to be radiographed. The cassette and its supporting tray are positioned in the path of the X-ray beam and the radiograph exposure is then taken.
2. The Prior Art
With typical prior devices, there have been a number of disadvantages. Most of these disadvantages are inherent in or related to the X-ray film cassettes. As compared with the method and apparatus of the present invention, the cassettes are cumbersome, expensive, time-consuming in use, and of poor reliability.
The typical cassette has a marginal metal frame. One side of the frame, the side to be positioned toward the X-ray source, is closed by a face plate composed of an X-ray transparent sheet. This face plate is secured to the frame in a light-tight manner. The radiographic film is positioned between two fluoroscopic screens known as intensifying screens. This "sandwich" of screens and film is inserted into the cassette and a closure plate is then clamped in position to squeeze the intensifying screens and the X-ray film into tight intimate contact with one another between the face and closure plates. Pressure springs are used to maintain this intimate contact.
These described prior art cassettes have a number of disadvantages. A principal disadvantage is too frequently the necessary intimate contact between the intensifying screens and the radiographic film is lost. This loss of contact may result from a number of causes such as fatigue or improper positioning of the pressure springs. The result is either a poor or a totally unusable radiograph. At times it is necessary to return the patient to the radiographic table and repeat part or all of the radiographic series because of cassette failure.
While the problem of lack of intimate contact between the radiographic film and the intensifying screens has been overcome for many applications with the evacuated cassette structure taught in the above referenced U.S. Pat. No. 3,348,042, the disclosure in that application does not overcome many other disadvantages which are obviated by this invention.
In the referenced application, the technique employed is to insert intensifying screens with a sheet of radiographic film between them and then to evacuate and seal that envelope. It will be recognized that this evacuating technique and the conventional cassette loading techniques described above are relatively difficult and time consuming. Moreover, the loading must be performed in a dark room. Similarly, the unloading of these cassettes is time consuming and must be performed in a dark room.
With prior arrangements the intensifying screens are handled twice for each radiograph, once in the loading and once in the unloading operation. This is not only a factor which contributes to the unnecessary consumption of time with the prior devices but is a further disadvantage because the inevitable result is that these relatively expensive screens have relatively short useful lives.
For a number of reasons, a variety of sizes of radiographs are frequently used. Since a variety of sizes of radiographs are used, it is preferable that a sheet of film be of appropriate size for the exposure. Customarily, a cassette and intensifying screen of a size corresponding to the film size are used. Accordingly, each hospital or X-ray clinic must maintain a substantial inventory of loaded cassettes in or quickly available to each X-ray room. In spite of this, delays are frequently experienced while the operator waits to obtain a cassette of appropriate size or a radiograph is made on an inappropriate size of film. The cassette handling problem is of such magnitude that complicated cassette conveying mechanisms are built integrally into the walls of some new hospitals so that loaded and exposed cassettes can be transported to and from an X-ray room mechanically.
Another problem inherent in the use of any cassette under a radiographic table is the problem of centering the cassette in the X-ray beam. One of the more acceptable prior solutions for this problem is the solution described and claimed in U.S. Pat. No. 2,887,586, issued May 19, 1959, to Walter Reiniger entitled, "X-Ray Focusing Apparatus." With the method and apparatus taught in that patent, a beam of light which coincides with the center of the X-ray beam is projected downwardly onto the X-ray table. The cassette tray is pulled outwardly of the X-ray table and shifted longitudinally of the table until the center of the tray and its cassette is in the path of the beam. The tray is then pushed under the table and a radiograph is taken, but not until an additional procedure is carried out of positioning the anatomical part concerned under the center of the X-ray beam.
Where the cassette is to be positioned centrally of the table, a magnetic centering of the X-ray tube described and claimed in U.S. Pat. No. 2,823,315, issued Feb. 11, 1958, under the title "X-Ray Apparatus and Control" to R. J. Stava et al, solves the problem providing the operator very carefully centers the cassette in the tray under the table. Prior to this invention, however, there has been no mechanism which automatically centers relatively the X-ray source and a radiographic film of a selected one of a plurality of sizes, positioned beneath an X-ray table.
In the past, there have been proposals for feeding film, one sheet at a time, from a storage device to an exposure position and then to an exposed film magazine. These proposals have not been fully satisfactory and have had a number of inherent disadvantages overcome by the present invention. Among these disadvantages have been: (1) The proposed mechanisms were not constructed to assure the necessary complete intimate contact between the intensifying screens and the film under all conditions; (2) No provision was made for using a radiographic film of a selected one of a plurality of film sizes; and, (3) No provision was made for automatically centering an X-ray tube with respect to the film or vice versa.
Since these proposed devices were capable of only using a film of a single size, even when operating properly, they were also unsatisfactory because of the inherent expense in wasting radiographic film. Additionally, the quality of radiographs produced on a mechanism of any such prior proposal was not of a level produced by the method and apparatus of this invention.